Auscultation of the heart is a well-defined and standard component of the physical examinations of patients. It is typically performed with a commercially available stethoscope. Physicians perform auscultation by listening to heart sounds desirably, in sequence, at a set of well-defined sites on the chest surfaces. These sites are typically defined with reference to anatomical landmarks, such as the second intercostal space on the left, etc. They may also be defined based on the heart valve preferentially heard at that location (i.e., aortic, pulmonic, etc.). Additionally, auscultation can be carried out with the patient in different postures, or while executing various maneuvers that are designed to enhance or suppress certain murmurs.
Auscultation of the heart is a difficult procedure, involving significant training. Stethoscopes transfer only a small fraction of the acoustic signal at the chest surface to the listener's ears and filter the cardiac acoustic signal in the process. A significant portion of the signal energy in heart sounds is at frequencies below the frequency range of human hearing, and this situation only tends to worsen with increased age of the listener. Thus, as a physician's auscultatory skill increases, his hearing may still limit his ability.
Also, auscultation relies on determining the correct sequence of brief events that are closely spaced in time, a determination that may be difficult for human listeners. Furthermore, auscultation relies on determining the correspondence of the primary heart sounds with the length of the systolic and diastolic phase of the heart. This becomes more difficult when the systolic and diastolic intervals are more equal, which typically occurs at elevated heart rates.
The practice and teaching of the clinical skill of auscultation of the heart has declined among physicians. Learning auscultation is complicated by the reliance of diagnostic instructional manuals that rely on subjective descriptions of heart sounds, which require much practice to appreciate. Recent tests have demonstrated that many physicians can reliably identify only a small number of standard heart sounds and murmurs, as described by Burdick et al., in “Physical Diagnosis Skills of Physicians in Training: A Focused Assessment,” Acad. Emerg. Med., 2(7), pp. 622-29, July 1995; Mangione et al., in “Cardiac Auscultatory Skills of Internal Medicine and Family Practice Trainees: A Comparison of Diagnostic Proficiency,” Journal of the American Medical Association, 278(9), pp. 717-22, September 1997; and Gracely et al., in the Teaching and Practice of Cardiac Auscultation During Internal Medicine and Cardiology Training: A Nationwide Survey,” Annals of Internal Medicine, 119(1), pp. 47-54, July 1993. Consequently, serious heart murmurs in many patients may go undetected by physicians relying on standard auscultation technique.
This decline in auscultation skills has led to an over-reliance on echocardiography, resulting in a large number of unnecessary and expensive diagnostic studies. Thus, economic factors have also lead to an interest in improving auscultatory screening procedures. One approach that has generated interest is the use of electronic stethoscopes. These electronic stethoscopes may improve auscultation procedures by amplifying and/or filtering sounds detected during auscultation, helping the physician to hear the important bodily sounds. The use of electronic stethoscopes in auscultation may also allow the recording of heart sounds for automated analysis to assist the physician in making a diagnosis.
Particularly, in the area of automated analysis of auscultatory data, it is important to known the characteristics of the electronic stethoscope, or other sound recording device, being used. The present invention involves an apparatus and test procedures to test the response characteristics of an electronic stethoscope.